Top gallants are extra sails at the top of a mast, giving the ship more sail area and therefore a higher speed.

All sailing ships rely on the wind for motive power. The only practical way to make a better speed through the water at a particular wind velocity is to put on more sail. Each mast is designed to take a main sail and a topsail, but it is possible with top gallants to add an extra sail above the topsail. Naturally, this requires more yards, ropes and skilled sailors to set the sails. Adding a top gallant is also something of a strain on the fabric of the ship: the extra strain on a mast can, in high winds, rip it right out of a hull. This catastrophic damage to the whole ship can also cause casualties among the crew.

The speed and handling of a ship can also be improved by careening the hull: a process that takes days. This, however, is not something that will instantly give more speed, unlike setting the topgallants.

Top Gallants increase the top speed of ships by 1 or 2; lighter ships gain a larger bonus. Top Gallants are the only technology that increases the speed of ships in Napoleon: Total War. While most ships use top gallants once they are researched, some (such as Dhows and Galleys) do not. Captured ships that have top gallants retain their benefits even after changing hands.